The Effect of Hybrid Treatment Combining Boriding and Nanobainitising on the Tribological and Mechanical Properties of 66SiMnCrMo6-6-4 Bearing Steel

Abstract

The effect of a new hybrid heat treatment consisting of pack-boriding and nanobainitising on the microstructure and properties of EN 66SiMnCrMo6-6-4 bearing steel was investigated. The hybrid treatment produces a new high-strength (ca. 1480 MPa) material with a hard boride (ca. 2000 HV0.05) surface layer and a relatively ductile nanobainitic core. The formation of the boride layer significantly improves wear resistance. The boride layer, which is hard but susceptible to cracking, reduces the mechanical properties under tensile and impact loads. However, the borided and nanobainitised steel exhibits much higher tensile strength and ductility and slightly better impact toughness than steel after post-boriding quenching and tempering.

The Effect of Chemical Composition on the Microstructure and Properties of Multicomponent Nickel-Based Boride Layers Produced on C45 Steel by the Hybrid Method

“…The cause of structural changes in the substrate in the vicinity of the boride layer is most likely local increases in the concentration of silicon and carbon rejected down into the substrate by the growing boride. Such a phenomenon was observed in the borided high alloy nanobainitic steels we recently investigated [28,29]. The formation of the pearlitic zone results from the substrate's enrichment with carbon due to pushing by the forming layer of borides, which do not dissolve carbon.…”

“…The inspiration for the present study was our recent work on the application of boriding in the surface engineering of nanobainitic steel [28,29]. Although, as demonstrated, boriding can be effectively combined with advanced steel heat treatments such as nanobainitising, the porosity, the FeB formation-related brittleness, and relatively low wear resistance of the layers based on iron borides limit the achieved improvement effect.…”